PubMed · 378254
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R H Seville, G B Walker, M Whitefield. 1979. Dithranol cream.. https://doi.org/10.1111/j.1365-2133.1979.tb01654.x
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The interaction of the tetramisole derivative (+-)-5,6-dihydro-6-phenyl-imidazo[2,1-b]thiazole and a number of its 2-n-alkyl homologues (-ethyl through -n-pentyl and -n-heptyl) with large unilamellar phosphatidylcholine/phosphatidylethanolamine/dipalmitoylphosphatidic acid (2:1:0.06, w/w) vesicles was studied by means of steady-state fluorescence quenching using 8-(2-anthryl)octanoic acid as membrane probe. Linear Stern-Volmer plots were obtained for each derivative, indicating dynamic quenching. The slopes of the plots decreased with increasing liposomal concentration. For four short-chain homologues (-H, -ethyl, -n-propyl and -n-butyl), the respective membrane partition coefficients Kp and bimolecular quenching rate constants kq were determined from the plots of the reciprocal of the apparent quenching rate constant (kappq)-1 against the lipid volume fraction alpha L of the liposomes. The partition coefficients increased with increasing chain-length of the tetramisoles. A linear relationship was found between the free energy of partitioning and the number of methylene units of the homologues (-delta G degrees per methylene group = 1.6 +/- 0.1 kJ mol-1). For the n-pentyl and n-heptyl derivatives, the fluorescence quenching technique did not allow one to determine their membrane partition coefficients. Analysis of the fluorescence intensity measurements with Scatchard plots gave further evidence for the partitioning nature of the tetramisole derivatives' association with the liposomal membranes.
Diels-Alder heterocycloaddition reactions of 2,5,8-quinolinetriones and 1-azadienes afford 1,8-diaza-2,9,10-anthracenetriones, which are simple analogues of the antitumoral antibiotic diazaquinomicin A. Cytotoxicity in this series and antitumor activity of the lead compound, 6-methyl-1,8-diaza-2,9,10-anthracenetrione, are reported.
Fluorescence quenching has been used to study the partition of the tetramisole derivative (+-)-5,6-dihydro-6-phenyl-2-n-propyl-imidazo[2,1-b]thiazole into liposomes, consisting of a mixture of egg L-alpha-phosphatidylcholine, egg phosphatidylethanolamine and dipalmitoylphosphatidic acid (2:1:0.06 w/w/w). The tetramisole derivative quenched the fluorescence of the intramembrane probe 8-(2-anthryl)-octanoic acid. The quenching process could be rationalized by a model for dynamic quenching in which an intermediate excited-state non-emitting complex (PQ)* between neutral quencher (Q) and excited probe (P*) is involved: [sequence: see text] where kd, k-d and ki represent the rate constants of complex formation, dissociation and deactivation, respectively. The subscripts A and L denote the aqueous and lipid phases, and the asterisk indicates the excited state. Linear Stern-Volmer plots were obtained from quenching experiments of fluorescence intensities and fluorescence life-times. The slopes of the plots were dependent on the lipid volume fraction of the liposomes. Measurement of the reciprocal of the apparent bimolecular quenching rate constant at various lipid volume fractions yielded the partition coefficient Kp and the overall quenching rate constant kq[kq = kdki/(ki+k-d)] of the tetramisole derivative. The steady-state measurements were performed at three different pH-values. Time-correlated single photon counting measurements revealed a single-exponential fluorescence decay for 8-(2-anthryl)-octanoic acid in the presence and absence of quencher. The quenching results were in accordance with the model that only the neutral form is capable of partitioning into the lipid phase. Combined average values of 318 and 6.59 x 10(8) M-1s-1 were calculated for the partition coefficient and the bimolecular quenching rate constant, respectively, from the steady-state and time-resolved quenching experiments.